The present invention relates to thermoplastic fluoropolymers having improved mechanical properties in combination with low permeability to gases and water vapour, optionally with improved processability.
Specifically the present invention relates to thermoplastic fluoropolymers formed by copolymers based on chlorotrifluoroethylene (PCTFE) and by copolymers based on ethylene/chlorotrifluoroethylene (ECTFE) and/or ethylene/tetrafluoroethylene (ETFE).
The polymers of the invention are to be used to obtain pipes, sheets, molded articles and above all films to be used for example in the packaging industry and more specifically in the food and pharmaceutical industry.
It is known in the prior art that PCTFE is a fluorinated resin having a good chemical resistance characterized by very good properties of impermeability to gases and vapours, more specifically to oxygen, nitrogen and water vapour. These PCTFE copolymers have however poor mechanical properties, typical of a brittle material, i.e. high values of elastic modulus and yield stress combined with poor stress and strain at break.
As known the PCTFE polymers having a high molecular weight show better mechanical properties than those having a low viscosity. However the processing of fluoropolymers (e.g. PCTFE) having a very high viscosity is extremely difficult for the obtainment of pipes, sheets, films and molded articles.
The need was therefore felt to have available fluoropolymers having a very good impermeability to gases and vapours combined with improved mechanical properties, i.e. higher values of stress and strain at break, preferably having good processability.
The Applicant has surprisingly and unexpectedly found fluoropolymers having the above mentioned properties.
An object of the preent invention is a polymer composition comprising: (A) (co)polymers based on chlorotrifluoroethylene (PCTFE) and (B) (co)polymers based on ethylene/chlorotrifluoroethylene (ECTFE) and/or ethylene/tetrafluoroethylene (ETFE), wherein the E:CTFE (or TFE) ratio by moles is between 1:3 and 3:1. Preferably the amount of the (co)polymer based on chlorotrifluoroethylene (PCTFE) in the polymer composition is at least 5% by weight, more preferably at least 20% by weight, still more preferably at least 40% by weight.
The PCTFE (co)polymers according to the present invention contain at least 99% by moles of chlorotrifluoroethylene (CTFE) being the complement to 100 one or more fluorinated or non-fluorinated monomers. Among fluorinated monomers, (per)fluoropropylvinylether and (per)fluorodioxoles, as described in European patent applications EP 1.067,145 and EP 1,067,148, can for example be mentioned. Among non-fluorinated monomers, acrylic monomers as described in EP-A-964010 can for example be mentioned. Preferably PCTFE is the CTFE homopolymer (as described in European patent application EP 1,067,146). The PCTFE homopolymer having a Melt Flow Index (MFI) lower than 10.0 g/10xe2x80x2 measured at 265xc2x0 C. and at 10 Kg load according to the ASTM D 1238-88 method is still more preferred.
The (co)polymers (B) ECTFE or ETFE according to the present invention are preferably formed by:
(a) from 35 to 65%, preferably from 45 to 55%, more preferably from 48 to 52% by moles of ethylene (E),
(b) from 65 to 35%, preferably from 55 to 45%, more preferably from 52 to 48% by moles of chlorotrifluoroethylene (CTFE) (for the ECTFE copolymers) or tetrafluoroethylene (TFE) (for the ETFE copolymers), and optionally
(c) from 0.1 to 30%, by moles, preferably 0.1-10, more preferably 0.1-5 based on the total amount of monomers (a) and (b), of one or more fluorinated or non-fluorinated monomers. Among fluorinated monomers we can for example mention (per)fluoroalkylvinylethers (perfluoropropylvinylether), (per)fluorodioxoles as described in U.S. Pat. No. 5,597,880), vinylidenefluoride (VDF). Among non-fluorinated monomers, the hydrogenated monomers having the general formula:
CH2xe2x95x90CHxe2x80x94(CH2)nxe2x80x94R1xe2x80x83xe2x80x83(I) 
can be mentioned, wherein R1xe2x95x90OR2, or xe2x80x94(O)tCO(O)pR2 wherein t and p are integers equal to 0, 1 and R2 is a hydrogenated radical C1-C20 from 1 to 20 carbon atoms, of alkyl type, linear or branched when possible, or cycloalkyl, optionally containing heteroatoms and/or chlorine atoms, the heteroatoms preferably being O or N, R2 optionally contains one or more functional groups, preferably selected from OH, COOH, epoxide, ester and ether, R2 optionally contains double bonds, or R2 is H, n is an integer in the range 0-10.
Preferably R2 is of alkyl type from 1 to 10 carbon atoms containing functional groups of hydroxide type, n is an integer in the range 0-5.
The preferred comonomers (c) are for example selected from the following classes:
1) Acrylic monomers having the general formula:
CH2xe2x95x90CHxe2x80x94COxe2x80x94Oxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Ethylacrylate, n-butylacrylate, acrylic acid, hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy) ethylhexylacrylate, etc. can for example be mentioned.
2) Vinylether monomers having the general formula:
CH2xe2x95x90CHxe2x80x94Oxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Propylvinylether, cyclohexylvinylether, vinyl-4-hydroxybutylether, etc. can for example be mentioned.
3) Vinyl monomers of the carboxylic acid having the general formula:
CH2xe2x95x90CHxe2x80x94Oxe2x80x94COxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Vinyl-acetate, vinylpropionate, vinyl-2-ethylhexanoate, etc. can for example be mentioned.
4) Unsaturated carboxylic acids having the general formula:
CH2xe2x95x90CHxe2x80x94(CH2)nxe2x80x94COOH 
wherein n has the above mentioned meaning. For example vinylacetic acid, etc.
The preferred (co)polymers of component (B) of the polymer composition of the invention are based on ethylene/chlorotrifluoroethylene (ECTFE) (co)polymers.
It has been found by the Applicant that to obtain also a good processability in combination with the other above mentioned properties of the polymer composition, the component (B) is an ECTFE having a Melt Flow Index (MFI) higher than 5 g/10xe2x80x2, preferably higher than 10 g/10xe2x80x2 measured at 275xc2x0 C. and at 2.16 Kg load (according to the ASTM 3275-89 method).
Another object is a process for the preparation of the polymer composition according to the present invention based on PCTFE and ECTFE or ETFE. For example a preferable process is the radical synthesis of the ECTFE or ETFE (co)polymer (B) in the presence of the PCTFE (co)polymer (A), or the radical synthesis of the PCTFE (co) polymer (A) in the presence of the ECTFE or ETFE (co) polymer (B). These syntheses, (co)polymerizations, are carried out in the presence of radical initiators, in suspension in organic medium or in aqueous emulsion, at a temperature between xe2x88x9260xc2x0 and 150xc2x0 C., preferably xe2x88x9220xc2x0 and 100xc2x0 C., more preferably xe2x88x9210xc2x0 and 50xc2x0 C., and at a reaction pressure in the range 0.5-100 bar, preferably 5-40 bar.
Among the radical initiators that can be in particular used are:
(i) bis-acylperoxides of formula (Rfxe2x80x94COxe2x80x94O)2, wherein Rf is a (per)haloalkyl C1-C10 (see for example EP 185,242 and U.S. Pat. No. 4,513,129), or a perfluoropolyoxyalkylene group (see for example EP 186,215 and U.S. Pat. No. 5,021,516); among them, bis-trichloroacetylperoxide and bis-dichlorofluoroacetylperoxide (see U.S. Pat. No. 5,569,728) are particularly preferred;
(ii) dialkylperoxides of formula (RHxe2x80x94O)2, wherein RH is an alkyl C1-C10; diterbutylperoxide (DTBP) is particularly preferred;
(iii) inorganic peroxides soluble in water, such as ammonium or alkaline metal persulphates or perphosphates; sodium and potassium persulphates are particularly preferred;
(iv) dialkylperoxydicarbonates, wherein the alkyl has from 1 to 8 carbon atoms, such as for example di-n-propyl-peroxydicarbonate and di-isopropyl-peroxydicarbonate (see EP 526,216);
(v) organic or inorganic redox systems, such as ammonium persulphate/sodium sulphite, hydrogen peroxide/aminoiminomethansulphinic acid, terbutylhydroperoxide/methabisulphite (see U.S. Pat. No. 5,453,477).
(vi) photoinitiators activated by UV radiation such as inorganic and organic peroxides, halogenated and polyhalogenated organic compounds (see EP 650,982, U.S. Pat. No. 5,688,838).
In the case of the copolymerization in suspension, the reaction medium is formed by an organic phase, to which water is added in order to favour the heat dispersion developed during the reaction. The organic phase can be formed by the monomers themselves, without addition of solvents, or by the monomers dissolved in a suitable organic solvent. Among solvents we can mention branched chain hydrocarbons described in U.S. Pat. No. 5,434,229, having from 6 to 25 carbon atoms and a ratio between methyl groups and number of carbon atoms higher than 0.5, such as for example 2,3-dimethylbutane, 2,3-dimethylpentane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4,6-pentamethylheptane, etc, or mixtures thereof. Other organic solvents are chlorofluorocarbons, such as CC12F2 (CFC-12), CCl3F (CFC-11), CCl2FCClF2 (CFC-113), CClF2CClF2 (CFC-114), etc. Since said products have a destroying effect on the ozone present in the stratosphere, alternative products, such as the compounds containing only carbon, fluorine, hydrogen, and optionally oxygen, described in U.S. Pat. No. 5,182,342, have recently been suggested.
In particular (per)fluoropolyethers with at least one hydrogenated end group, preferably two, of the xe2x80x94CF2H, xe2x80x94CF2CF2H, xe2x80x94CF(CF3)H type can be used.
In the case of the copolymerization in aqueous emulsion it is carried out in the presence of one or more fluorinated surfactants.
The most commonly used fluorinated surfactants are those of general formula:
Rfxe2x80x94Xxe2x88x92 M+
wherein Rf is a (per) fluoroalkyl chain C5-C16 or a (per) fluoropolyoxyalkylene chain, Xxe2x88x92 is xe2x80x94COOxe2x88x92 or xe2x80x94SO3xe2x88x92, M+ is selected from: H+, NH4+, an alkaline metal ion. Among them we mention: ammonium and/or sodium perfluoro-octanoate, (per)fluoropolyoxyalkylenes ended with one or more carboxylic groups, etc.
The process object of the present invention can be advantageously carried out in the presence of dispersions, emulsions or microemulsions preferably of perfluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006, or also of microemulsions preferably of fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated repeating units, according to U.S. Pat. No. 5,498,680 in the name of the Applicant.
In the case of the copolymerization of ECTFE or ETFE in the presence of PCTFE (co)polymers, the molecular weight control of the ECTFE or ETFE (co)polymer can be made by using specific chain transfer agents. Among these it can be mentioned: ketones, esters, ethers or aliphatic alcohols having from 3 to 10 carbon atomns; hydrocarbons or halogenated hydrocarbons, having from 1 to 6 carbon atoms; bis(alkyl)carbonates wherein the alkyl has from 1 to 5 carbon atoms, etc. Among them chloroform and alkyl substituted cyclopentanes (see U.S. Pat. No. 5,510,435), in particular methylcyclopentane, are particularly preferred. The transfer agent is fed to the reactor at the beginning of the reaction, or in a continuous way or in discrete amounts during the polymerization. The amount of the used chain transfer agent can range within rather wide limits, depending on the type of the monomers, the reaction temperature and the molecular weight requested.
Generally, said amount ranges between 0.01 and 30% by weight, preferably between 0.05 and 10% by weight, based on the total amount of monomers fed into the reactor.
The preferred process for the preparation of the polymer composition of the invention based on PCTFE and ECTFE or ETFE is characterized in that both (co)polymers, first PCTFE and then ECTFE or ETFE, or viceversa, are synthetized in sequence in the same reaction medium, both in suspension or in emulsion, or the PCTFE and ECTFE or ETFE (co) polymer is added under the form of powder or latex in the reaction medium before and/or during the radical synthesis.
The preferred process according to the present invention is the one in which the ECTFE or ETFE copolymer is synthetized in the presence of the PCTFE (co)polymer.
Besides it has been found by the Applicant that, in the specific case of the ECTFE or ETFE copolymer (B) synthesis in organic suspension in presence of water and of a PCTFE (co)polymer (A), the polymer composition of the invention is obtained without polymer build-up in the reactor, even when the component (B) has a low cristallinity.
Said PCTFE can be added under the form of powder or latex which coagulates by adding a coagulant in the reaction medium in the presence of the organic and aqueous phase. The coagulants of PCTFE are those known in the coagulation of the fluoropolymer latexes, for example aluminum sulphate, nitric acid, hydrochloric acid, calcium chloride. Calcium chloride is preferred. The amount of the coagulants depends on the type of the used coagulant. Amounts in the range 0.001%-30% by weight with respect to the total amount of water in the reaction medium, preferably in the range 0.01%-5% by weight, can be used.
The PCTFE addition under the form of latex at the beginning and/or during the (co)polymer (B) synthesis is preferred.
The PCTFE latex can be obtained by (co)polymerization in aqueous emulsion in the presence of a suitable surfactant as above mentioned.
The viscosity measurement of the polymers object of the present invention is made by the Melt Flow Index (MFI) at 265xc2x0 C. and at 10 Kg load according to the ASTM D1238-88 method.
The percentage by weight of the PCTFE (co)polymer in the polymer composition is determined by mass balance.
The mechanical properties at 23xc2x0 C., have been obtained according to the ASTM D1708 method by using compression molded test specimens.
The permeability to oxygen has been determined according to the ASTM D1434 method at room temperature (23.5xc2x10.2xc2x0 C.) by using compression molded sheets having a nominal thickness of 0.3 mm.
Some embodiment Examples of the present invention are hereinafter reported, the purpose of which is merely illustrative but not limitative of the scope of the invention itself.